14 May 1796: Edward Jenner performs his first vaccination

For James Phipps, being a healthy eight-year-old boy in 1796 had its hazards. He was the son of British doctor and physician Edward Jenner's gardener, which also made him his lab rat.

Jenner had a theory he couldn't wait to test out, and that May, the opportunity arose. A milkmaid named Sarah Nelmes visited Jenner fearing she had contracted smallpox – a disease that often resulted in death. So you can imagine her relief when Jenner diagnosed her with the milder cowpox, which she had caught off the long-lashed Blossom. Having extracted some of the fluid from her infected hand, Jenner went to pay the young Phipps a visit.

It had long been noticed that sufferers of cowpox never caught smallpox. In 1774, a Benjamin Jesty had even infected his family with cowpox in the belief that it would save their lives when smallpox swept through the area. So, in that sense, Jenner didn't “invent” vaccinations, but he was the first to study their effects.

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To do so, he made two small incisions in the arm of young Phipps and rubbed in the cowpox fluid. Then he waited. Right on cue, Phipps fell ill with cowpox, and after a week, he was better. But of course, Jenner wasn't finished.

Taking hold of the long-suffering Phipps, he exposed him to the far deadlier smallpox. Thankfully, young Phipps was immune, if also a little fed up. But Jenner's vaccinations, which he named after the Latin word for cow, were a hard sell. He still couldn't explain why it worked, and many people believed the vaccination would cause them to grow horns.

In 1979, the World Health Organisation (WHO) declared smallpox eradicated after decades of tracking and containing the disease, saving millions of lives. And of course, the financial savings have been significant too.

According to The Center for Global Development, a US think tank, the annual cost of the smallpox campaign between 1967 and 1979 was US$23 million. "The US saves the total of all its contributions every 26 days because it does not have to vaccinate or treat the disease."

Visitors to the WHO website will be relieved to learn that the smallpox virus now only exists in two "secure laboratories" in Russia and the US. But just last year, several forgotten vials of the deadly pathogen were found languishing at the back of fridge in Maryland. Who knows how many more may be lurking out there?